The present invention relates to an ink jet recording apparatus and, more particularly, to an ink jet recording apparatus having means for controlling the amount of ink jetted towards a recording medium.
An ink jet recording apparatus has heretofore been used as a device for delineating a line, character or figure by the utilization of fine droplets of ink successively jetted from an ink tank through a fine nozzle. By way of example, where this type of ink jet recording apparatus is employed in an X-Y plotter, ink within the ink tank is jetted in the form of fine droplets through the nozzle at a relatively high frequency towards the recording medium so that the ink droplets deposited on the recording medium will form a continuous line.
U.S. Pat. No. 3,968,498, patented on July 6, 1976, for example, discloses an ink jet recording apparatus employed in an X-Y plotter. In general, since the ink jet recording apparatus intended for use in the X-Y plotter is required to satisfy the requirement that initiation and interruption of the jetting of ink must precisely respond to the presence and absence of a command signal (which corresponds to UP-DOWN signals employed in an X-Y plotter of a type utilizing a writing pen, which UP-DOWN signals are selectively used to disengage and engage the tip of the writing pen from and to the recording medium), an ink jet recording apparatus of the non-impact recording type wherein application of electric voltage between the nozzle and an electrode positioned in the vicinity of the nozzle results in jetting of ink from the nozzle towards the recording medium is recommended for use in the X-Y plotter.
In the above numbered U.S. patent, the statement has been made that, where the ink jet recording apparatus is employed in the X-Y plotter, a resultant delineated line of uniform width cannot be obtained unless the amount of ink jetted is caused to vary with change in recording velocity. Starting from this problem, the above numbered U.S. patent discloses concrete means for solving the above described problem, such as by the employment of a technique wherein the voltage to be applied between the nozzle and the electrode is made proportional to the recording velocity, a technique wherein the frequency of vibrations applied to the ink within the ink tank is made proportional to the recording velocity or a combination of these techniques.
However, it has been found that the voltage applied between the nozzle and the electrode and the amount of ink jetted has a proportional relationship only within a limited range. Moreover, it has also been found that the employment of a method wherein vibrations or pulsating pressures are applied to the ink within the ink tank has a disadvantage that an exact proportional relationship cannot be obtained between the pressure and the amount of ink jetted and that the recording head and its related parts are adversely affected by such vibrations.
Furthermore, in the conventional method particularly wherein pressure is applied to the ink within the ink tank during jetting of the ink, since actual measurement of the pressure thus applied is not made, a precise control of the amount of ink jetted is not achieved. Moreover, the conventional ink jet recording apparatus wherein vibrations are employed to apply the pressure to the ink is not suited for delineating a line since the frequency or speed of formation of the ink droplets is very low.
Where control of the amount of ink jetted is effected in the manner as herinabove described in the conventional ink jet recording apparatus, no consideration has been paid to the relationship between the change in viscosity of the ink resulting from a change in temperature, the amount of ink within the ink tank, the pressure acting on the ink and the voltage applied between the nozzle and the electrode, all of which have been found to affect the amount of ink being jetted from the nozzle towards the recording medium.
Moreover, in the case where the ink jet recording apparatus is to be employed in the X-Y plotter, although the employment of a control technique necessary to control the amount of ink jetted so that a line of uniform width can be obtained without being substantially adversely affected by the recording velocity and other factors provides the possibility that lines of different width can be delineated on the recording medium one at a time with a single nozzle, such use has not yet been made of the conventional device.
In view of the foregoing, the use of a conventional ink jet recording apparatus involves various problems which must be solved in order for it to be satisfactory for an X-Y plotter.